Lubricity additives for fuel oil compositions

ABSTRACT

Specific substituted aromatic ester compounds are useful as lubricity additives for middle distillate fuel oils.

This application is a 371 of PCT /EP97/05105 Sep. 15, 1997

This invention relates to additives for improving the lubricity of fueloils such as diesel fuel oil. Diesel fuel oil compositions including theadditives of this invention exhibit improved lubricity and reducedengine wear.

Concern for the environment has resulted in moves to significantlyreduce the noxious components in emissions when fuel oils are burnt,particularly in engines such as diesel engines. Attempts are being made,for example, to minimise sulphur dioxide emissions. As a consequenceattempts are being made to minimise the sulphur content of fuel oils.For example, although typical diesel fuel oils have in the pastcontained 1% by weight or more of sulphur (expressed as elementalsulphur) it is now considered desirable to reduce the level to 0.2% byweight, preferably to 0.05% by weight and, advantageously, to less than0.01% by weight, particularly less than 0.001% by weight.

Additional refining of fuel oils, necessary to achieve these low sulphurlevels, often results in reductions in the level of polar components. Inaddition, refinery processes can reduce the level of polynucleararomatic compounds present in such fuel oils.

Reducing the level of one or more of the sulphur, polynuclear aromaticor polar components of diesel fuel oil can reduce the ability of the oilto lubricate the injection system of the engine so that, for example,the fuel injection pump of the engine fails relatively early in the lifeof an engine. Failure may occur in fuel injection systems such as highpressure rotary distributors, in-line pumps and injectors. The problemof poor lubricity in diesel fuel oils is likely to be exacerbated by thefuture engine developments aimed at further reducing emissions, whichwill have more exacting lubricity requirements than present engines. Forexample, the advent of high pressure unit injectors is anticipated toincrease the fuel oil lubricity requirement.

Similarly, poor lubricity can lead to wear problems in other mechanicaldevices dependent for lubrication on the natural lubricity of fuel oil.

Lubricity additives for fuel oils have been described in the art. WO94/17160 describes an additive which comprises an ester of a carboxylicacid and an alcohol wherein the acid has from 2 to 50 carbon atoms andthe alcohol has one or more carbon atoms. Glycerol monooleate isspecifically disclosed as an example. Acids of the formula “R¹ (COOH)”,wherein R¹ is an aromatic hydrocarbyl group are generically disclosedbut not exemplified.

U.S. Pat. No. 3,273,981 discloses a lubricity additive being a mixtureof A+B wherein A is a polybasic acid, or a polybasic acid ester made byreacting the acid with C1-C5 monohydric alcohols: while B is a partialester of a polyhydric alcohol and a fatty acid, for example glycerolmonooleate, sorbitan monooleate or pentaerythritol monooleate. Themixture finds application in jet fuels.

GB-A-1,505,302 describes ester combinations including, for example,glycerol monoesters and glycerol diesters as diesel fuel additives, thecombinations being described as leading to advantages including lesswear of the fuel-injection equipment, piston rings and cylinder liners.GB-A-1,505,302 is, however, concerned with overcoming the operationaldisadvantages of corrosion and wear by acidic combustion products,residues in the combustion chamber and in the exhaust system. Thedocument states that these disadvantages are due to incompletecombustion under certain operating conditions. Typical diesel fuelsavailable at the date of the document contained, for example, from 0.5to 1% by weight of sulphur, as elemental sulphur, based on the weight ofthe fuel.

U.S. Pat. No.3,287,273 describes lubricity additives which are reactionproducts of a dicarboxylic acid and an oil-insoluble glycol. The acid istypically predominantly a dimer of unsaturated fatty acids such aslinoleic or oleic acid, although minor proportions of the monomer acidmay also be present. Only alkane diols or oxa-alkane diols arespecifically suggested as the glycol reactant.

U.S. Pat. No. 4,090,971 describes amides of substituted hydoxyaromaticcarboxylic acids in which at least one substituent is ahydrocarbon-based radical containing at least about 10 carbon atoms,these materials being described as useful as dispersant additives. Theamides can be prepared via reaction of an ester intermediate with thecorresponding amine; vic-hydroxylalkyl esters of the acids are disclosedas suitable intermediates.

U.S. Pat. No. 5,089,158 describes derivatives of amides of an aromaticcarboxylic acid having an ortho-hydroxy group in the form of a salt witha multivalent metal ion. The amide precursors for such materials may beprepared via an ester intermediate formed by the reaction of therequisite carboxylic acid and a C1 to C6 alkanol, this ester then beingamidated by reaction with an amine.

U.S. Pat. No. 4,551,152 discloses that alcohol-containing fuels mayexhibit poor corrosion and wear, caused by the presence of alcoholsubstances. This alcohol-related problem is said to be inhibited by thepresence of an ester condensate. prepared from the reaction of a carboxyphenol with a polyol of the formula:

wherein a+c is 1-20 and b is 5-50, and subsequent reaction with analdehyde and ethylene diamine to form the condensate product.

U.S. Pat. No. 5,462,567 discloses poly(oxyalkylene) hydroxyaromaticesters according to a certain formula, wherein the ester group links apolyoxyalkylene substituent containing at least 5 oxyalkylene units withthe hydroxyaromatic ring. These compounds are described asdeposit-controlling additives for, inter alia, diesel fuels, when usedin combination with certain aliphatic amines.

U.S. Pat. No. 4,098,708 (filed in 1975 and published in 1978) describesesters of substituted hydroxyaromatic carboxylic acids in which at leastone substituent is a hydrocarbon-based radical containing at least about10 carbon atoms, with salicylic acid esters being preferred. The acidsare reacted with mono- or polyhydric hydrocarbon-based alcohols such asglycerol, pentaerythritol and a variety of glycols. The esters aredescribed as useful dispersant additives for lubricants andnormally—liquid fuels, such as diesel fuel or fuel oil according to ASTMSpecification D-395.

Such fuels typically contained much higher sulphur levels than thosewith which the present invention is concerned, as illustrated by thereferenced ASTM Specification which recites, for 1975, maximum sulphurlimits of as high as 0.5%. The corresponding ASTM Specification fordiesel fuel (D-975) recites limits of between 0.5 and 2.0% sulphur,depending on the intended end use of the fuel.

There exists in the art a continual need for lubricity additives showingenhanced performance over existing materials, due not only to thedevelopment of engines with more exacting requirements, but also to thegeneral demand from consumers and fuel producers for higher qualityfuels.

In addition, there is a desire for additives to be handleable withoutthe need for special operating measures. The extent to which an additivesolidifies at lower ambient temperatures (e.g. via crystallisation)determines the extent to which an additive may be handled in the absenceof heating and mixing procedures. Many conventional additives requiresubstantial mixing and heating prior to addition to the fuel, and suchoperations can cause processing delays and may make the use of suchadditives uneconomic in spite of their performance-enhancing effects.

Furthermore, there is an increasing need in the art for‘multifunctional’ additive compositions. Such compositions provide arange of performance-enhancing functions, typically through theincorporation therein of a number of individual additives each havingits own function. The resulting complex mixtures often require additionto the fuel in relatively large amounts, and may also suffer fromproblems of physical and chemical interaction between individualadditives which can impair their subsequent performance in the fuel. Theprovision of an individual additive with multiple performance-enhancingeffects can reduce or avoid the need for such complex compositions andtheir associated problems.

It has now been found that certain esters of specific substitutedaromatic carboxylic acids show improved lubricity performance overexisting additives, particularly those of WO 94/17160. These materialscan also display superior handleability. Some of these esters may alsoimpart other performance-enhancing effects to fuel oils.

In a first aspect, this invention provides a fuel composition obtainableby the addition of a minor proportion of a compound comprising one ormore aromatic ring systems wherein at least one of the ring systemsbears, as substituents;

(i) one or more hydrocarbon groups imparting oil solubility to thecompound, and

(ii) one or more hydroxyl groups or derivatives thereof or both, and

(iii) one or more ester groups of the formula

 wherein R″ represents an alkyl group optionally substituted by one ormore heteroatom-containing groups

to a major proportion of a liquid hydrocarbon middle distillate fuel oilhaving a sulphur concentration of 0.2% by weight or less, based on theweight of fuel.

In a second aspect, this invention provides a fuel oil compositionobtainable by the addition, to the fuel oil defined under the firstaspect, of an additive composition or concentrate into which has beenincorporated the compound defined under the first aspect.

In a third aspect, this invention provides a compound comprising one ormore aromatic ring systems, wherein at least one of the ring systemsbears, as substituents;

(i) one or more hydrocarbon groups imparting oil solubility to thecompound, and

(ii) one or more hydroxyl derivatives of the formula —OR′ wherein R′ ishydrocarbyl or a group of the formula

 wherein M represents an oxygen atom or an NH group and n represents anumber from 1 to 50, and

(iii) one or more ester groups of the formula

 wherein R″ represents an alkyl group optionally substituted by one ormore heteroatom-containing groups.

Further aspects of this invention include an additive composition intowhich has been incorporated the compound of the third aspect, and anadditive concentration obtainable by incorporating the compound oradditive composition and optionally one or more additional additives,into a mutually-compatible solvent therefor.

The compounds defined under the first aspect of the invention provide,upon addition to low sulphur fuel oil, an improvement in fuel oillubricity which can significantly exceed that obtainable from existinglubricity additives, and especially mixtures of the individual estersdisclosed in WO 94/17160, even when such existing additives are used insubstantially higher quantities (measured on an active-ingredientbasis).

In particular, the specific compounds defined under the first and secondaspects, and claimed under the third aspect, give higher lubricityperformance even at treat rates as low as 15 to 50 parts per million byweight, per weight of fuel oil. Furthermore, some of these compounds mayimpart other performance-enhancing features to fuel oils, particularlydetergency of engine fuel inlet systems and especially fuel injectors,reduced oxidation tendency especially during storage, and the ability todisperse insolubles which might otherwise give rise to harmful depositsand/or fuel line blockages. The detergency and dispersancy advantagesmay be apparent for those components wherein one or more of thesubstituents (ii) is a derivative of a hydroxyl group.

The Fuel Oil Composition of the First Aspect of the Invention

A The Compound

The compound may comprise one or more aromatic ring systems. By‘aromatic ring system’ in this specification is mean a planar cyclicmoiety which may be an aromatic homocyclic, heterocyclic or fusedpolycyclic assembly or a system where two or more such cyclic assembliesare joined to one another and in which the cyclic assemblies may be thesame or different. It is preferred that the or each aromatic ring systemis system based on heterocylic or homocyclic 5- or 6-membered rings,more preferably 6-membered rings and most preferably benzene rings.

The ring atoms in the aromatic system are preferably carbon atoms butmay for example include one or more heteroatoms such as N, S, or O inthe system in which case the compound is a heterocyclic compound.

Examples of suitable polycyclic assemblies include

(a) condensed benzene structures such as naphthalene, anthracene,phenanthrene, and pyrene;

(b) condensed ring structures where none of or not all of the rings arebenzene such as azulene, indene, hydroindene, fluorene, and diphenylene;

(c) rings joined “end-on” such as biphenyl; and

(d) heterocyclic compounds such as quinoline, indole, 2:3 dihydroindole,benzofuran, benzothiophen, carbazole and thiodiphenylamine.

Where the compound comprises only one aromatic ring system, this systemnecessarily bears all three types of substituent (i), (ii) and (iii). Itis preferred that one of each of the substituents (ii) and (iii) ispresent in such a compound. It is also preferred that one, two or threesubstituents (i) are present, at least one of which is capable ofimparting oil solubility to the compound.

Where the compound comprises two or more aromatic ring systems, it ispreferred that at least two, and preferably each, of the systems bearsall three types of substituent (i), (ii) and (iii). It is preferred thateach system bearing these three types of substituents bears one of eachof substituent (ii) and (iii), and preferably one, two or threesubstituents (i), subject to the requirement that at least one of thesubstituents (i) provides oil solubility to the compound.

Particularly preferred are compounds wherein the or each aromatic ringsystem is a single, 6-membered ring, especially a benzene structure.Most preferably, the compound comprises a single benzene ring and one,two or three (preferably one or two) of the substituents (i) and havingone of each of the (ii) and (iii) substituents, wherein substituent (ii)is a hydroxyl group.

Substituent (i) is a hydrocarbon group. By the term hydrocarbon as usedin this specification in relation to substituent (i) is meant an organicmoiety which is composed of hydrogen and carbon only, which is bonded tothe rest of the molecule by a carbon atom or atoms which unless thecontext states otherwise, may be aliphatic, including alicyclic,aromatic or a combination thereof. It may be substituted orunsubstituted alkyl, aryl or alkaryl and may optionally containunsaturation.

It is preferred that substituent (i) is aliphatic, for example alkyl oralkenyl, which may be branched or preferably straight-chain.Straight-chain alkyl is preferred.

It is essential for the good performance of the compound that at leastone substituent of the formula (i) be a hydrocarbon group of sufficientoleophilic character to impart oil solubility to the compound. In thisrespect, it is preferred that at least one substituent (i) contains atleast 8 carbon atoms, and preferably 10 to 200 carbon atoms. Asubstituent having 12 to 54, for example 14 to 36 carbon atoms isparticularly preferred. Most preferred are alkyl or alkenyl groupscontaining 12 to 54 carbon atoms, especially straight chain alkylgroups. The groups having 14 to 20 carbon atoms are most advantageous.

Provided that the compound possesses at least one hydrocarbonsubstituent (i) imparting the requisite oil solubility, any additionalsubstituents (i) may be of any character provided that they do notadversely interfere with the oil solubility of the compound.

Substituent (ii) is a hydroxyl group or derivative thereof, and can berepresented by the formula —OR′ . When a hydroxyl group, the compoundmay show particularly good performance as an oxidation inhibitor.

The hydroxyl group may be derivatised into a substituent capable ofimparting other multifuctional character, for example a group of theform —OR′ wherein R′ is hydrocarbyl, or a linear or branched chainalkyleneoxyhydrocarbyl or poly(alkyleneoxy)hydrocarbyl group and/or alinear or branched chain alkyleneaminohydrocarbyl or(polyalkyleneamino)hydrocarbyl group having the formula:

wherein M represents a oxygen atom or an NH group and n represents anumber from 1 to 50, preferably 2 to 20, more preferably 2 to 10, forexample 3 to 5. By the term hydrocarbyl in this specification is meantan organic moiety which is composed of hydrogen and carbon and which isbonded to the rest of the molecule by a carbon atom or atoms and whichincludes hydrocarbon groups as hereinbefore defined in relation tosubstituent (i), as well as predominantly-hdyrocarbon groups containingheteroatoms such as O, N or S provided that such heteroatoms areinsufficient to alter the essentially hydrocarbon nature of the group.The hydrocarbyl group in substitutent (ii) may especially besubstituted, preferably terminally substituted, by aheteroatom-containing group, for example a hydroxyl or amino group.Small hydrocarbyl groups, such as those containing1 to 24, preferably 1to 18, for example 2 to 12, are particularly advantageous. The alkylenegroup may contain 1 to 6, for example 2 to 4 methylene units and mayalso optionally be substituted by such a heteroatom containing group orgroups. R′ may be bonded directly to the oxygen depending from the ringsystem or indirectly via a linking group, such as a carbonyl group. Theheteroatom-containing derivatives of the hydroxyl group, useful assubstituent (ii), may be particularly beneficial in providing dispersantand/or detergent properties when used in fuel oils. Postulated in thisrespect are derivatives of the formula —O(CH₂)_(n′)—NH₂ wherein n′represents a number from 1 to 24, preferably 1 to 18, more preferably 2to 6.

Substituent (iii) is an ester group, wherein the carbonyl carbon of theester is bonded indirectly, or preferably directly, to a ring atom ofthe aromatic ring system and more preferably to a ring carbon. The estergroup is of the formula:

wherein the group —OR″ is derivable from the corresponding alcohol HOR″,wherein R″ represents an alkyl, preferably n-alkyl group, and especiallyone having 1 to 30, preferably 1 to 22, carbon atoms and optionallysubstituted by one or more heteroatom-containing groups, such ashydroxyl groups.

Particularly good results have been achieved when the alcohol HOR″ is amono or polyhydroxy alcanol, each hydroxyl group being bonded to adifferent carbon atom of the alcanol. Examples of suitable monohydroxyalcohols include C1 to C20 alkanols, for example methanol, ethanol,proponol, butanol and 2-ethyl hexanol. C1 to C10, for example C1 to C8,alkanols are preferred, the resulting ester group in the compound thuscomprising an alkyl substituent.

The most favoured alcohols are polyhydroxyalcanols giving rise in thecompound to ester groups comprising hydroxy-substituted alkylsubstituents. Suitable polyhydroxy alcanols are aliphatic, saturated orunsaturated, straight chain or branched alcohols having 2 to 10,preferably 2 to 6, more preferably 2 to 4, hydroxyl groups, and having 2to 90, preferably 2 to 30, more preferably 2 to 12, most preferably 2 to5, carbon atoms in the molecule. As examples, the polyhydroxy alcoholmay be a glycol or diol, or a trihydroxy alcohol. Ethylene glycol andglycerol are most highly preferred. Compounds comprising one or moresubstituents (iii) derived from such polyhydroxy alcanols have beenfound to exhibit particularly good lubricity activity at low treatrates.

In the compound, the substituents (ii) and (iii) are preferablypositioned vicinally on the aromatic ring system from which they depend.Where the system is polycyclic they are preferably positioned vicinallyon the same ring of the polycyclic system, for example in an orthoposition to each other, although they may be positioned on differentrings. The or each substituent (i) may be positioned vicinally to any ofthe substituents (ii) or (iii), or in a position further removed in thering system.

The compound may also be of oligomeric structure, such as a series ofaromatic ring systems connected via esterification with polyhydricalcohols, or via alkylene bridges produced, for example, by thephenol-formaldehyde type condensation reaction of several aromatic ringsystems with an aldehyde. Particularly useful are methylene-bridgedcompounds wherein each aromatic ring system is preferably a homocyclic,six-membered ring and wherein, more preferably, each ring carries atleast one of each of the substituents (i), (ii) and (iii).

A preferred form of the compound can be represented by the followinggeneral formula: (I)

wherein Ar represents an aromatic ring system, —B, —OR′ and —COOR″represent substituents (i), (ii) and (iii) respectively as hereinbeforedefined, and A represents a group of the formula (II):

wherein Ar, B, R′ and R″ are as hereinbefore defined in formula (I) andA′ and A″ each independently represent hydrocarbylene groups; andwherein:

v represents an integer in the range of from 0 to 10;

w represents an integer in the range of from 0 to 3;

and x, y and z each independently represent an integer in the range offrom 1 to 3.

Preferably, R′ represents hydrogen, or a hydrocarbyl group, or apoly(alkyleneoxy)alkyl or poly(alkyleneamino)alkyl group optionallysubstituted by one or more heteroatom-containing groups, and wherein R′may be bonded either directly to the oxygen depending from the ringsystem, or indirectly via a linking group; and R″ preferably representsa hydrocarbyl group optionally substituted by one or moreheteroatom-containing groups, or a poly(alkyleneoxy)alkyl orpoly(alkyleneamino)alkyl group, also optionally so substituted.

Preferably, x represents 1 or 2, especially when y and z eachrepresent 1. When w is 1 to 3, v is preferably 1 to 9, for example 2 to5, such as 3. Alternatively, v maybe 0 (zero). A′ and A″ are preferablymethylene or substituted methylene groups.

When w=o, the compound comprises a single aromatic ring system havingsubstituents (i), (ii) and (iii). It is preferred that when w=o, y and zeach=1 and x=1 or 2; more preferably, R″ represents an alkyl orhydroxylalkyl group and R′ represents hydrogen. Most preferably, Arrepresents a benzene ring; w=0; x=1 or 2; y and z each=1; R″ representsa hydroxylalkyl group and R′ represents hydrogen.

Most preferably, the compound is the ethylene glycol or glycerol esterof alkyl-substituted salicylic acid, the alkyl substituent orsubstituents of the acid containing between 14 and 18 carbon atoms.

The mechanism of action of the compound is not clearly understood.However, it is postulated that the specific substituted aromatic ringsystem or systems form a flat region within the molecule, the or eachhydroxyl or hydroxyl-derivatised group and ester group contributing toan electronic and polar character across this flat region which issurprisingly effective at surface adsorption and improving the fuels'ability to lubricate critical metal surfaces in the injection system,and particularly in the injection pump. Heteroatom substituents on theester group are also believed to contribute to additive performance.

The compound may be prepared by conventional means. Thus, for example,the compound may be prepared by esterification of a precursor compoundhaving the requisite aromatic ring system or systems bearingsubstituent(s) (i), substituent(s) (ii) and one or more carboxylic acidsubstituents, or acylating derivatives thereof, capable ofesterification with compounds having at least one hydroxyl group to formsubstituent (iii).

The esterification reaction is preferably performed in the presence ofan acidic or basic catalyst. Suitable acidic catalysts include sulphuricacid, paratoluene sulphonic acid or a macroreticular resin likeamberlyst with sulphonic acid groups. Suitable basic catalysts includeorganotitanates, e.g. titanium tetrabutoxide, organo zirconates orsodium methoxide.

Alternatively, and particularly when using polyhydroxyalcohols such asethylene glycol or glycerol, the esterification reaction may beperformed via a two-stage transesterification process. The acid is firstesterified with a simple, low boiling alcohol like methanol or butanol,and then transesterified using the desired polyhydroxyalcohol under basecatalysis, the low boiling alcohol being continuously removed bydistillation to drive the reaction.

A further alternative route for the formation of useful β-hydroxy estersis via a ring opening reaction of the reactant carboxylic acid compoundwith an epoxide, using a basic catalyst such as lithium hydroxide orcarbonate. This route is particularly suitable for the formation ofester groups equivalent to those derived from the reaction of the acidgroup with alcohols having hydroxy groups at both the 1-carbon and2-carbon positions, such as 1,2-dihydroxyethane (ethylene glycol) orglycerol. Suitable epoxides include 1,2-epoxyethane and1,2-epoxypropane, glicydol (2,3-epoxypropan-1-ol) or difunctionalcompounds such as the diglicydyl ether of ethylene glycol.

The precursor compound may itself be prepared by hydrocarbylation of asuitable hydroxyl-substituted aromatic ring system compound, for exampleby an electrophilic substitution reaction using a halide derivative ofthe desired hydrocarbyl substituent(s), for example via a Friedel-Craftstype reaction using iron (iii) chloride as catalyst. Alternatively,hydrocarbylation can be achieved through reaction of the correspondingalkene using a hydrogen fluoride and boron trifluoride catalyst system,or hydrogen chloride and aluminium trichloride catalyst system. Theresulting hydrocarbyl-substituted, hydroxyl-substituted aromaticcompound may be carboxylated, for example via the ‘Kolbe-Schmitt’reaction comprising the reaction of a salt, preferably an alkali metalsalt, of the hydrocarbyl substituted, hydroxyl-substituted aromaticcompound with carbon dioxide and subsequently acidifying the salt thusobtained. Alternatively, a Friedel-Crafts acylation-type reactionproduct may be used to add the required carboxylic acid substituent(s).This acid may be derivatised into an acylating group such as an acidhalide group, for example an acid chloride group, order to facilitatethe subsequent esterification reaction. The above types of reaction arewell-known in the chemical art.

The preferred precursor compounds are carboxylic acid derivatives ofhydrocarbyl-substituted phenols and/or napthols, with phenols being themost preferred. Particularly preferred are the hydrocarbyl-substitutedsalicylic acids, which typically comprise a mixture of mono anddisubstituted acids. These materials are readily available in a formsuitable for the esterification reaction, without the need for furthermodification.

During the esterfication reaction, incomplete conversion to the esterproduct(s) may result, especially when the precursor compound is acarboxylic acid rather than an acylating derivative thereof. The degreeof esterification can be monitored during the reaction, for example bytotal acid number (TAN-ASTM D-974/95).

It is preferred that the degree of esterification is at least 10%,preferably at least 30%, and more preferably at least 30%, by weight ofthe original amount of acid or derivative reactant acid. Good resultshave been obtained in the range of 70-90% esterification.

B The Middle Distillate Fuel Oil

The fuel oil has a sulphur concentration of 0.2% by weight or less basedon the weight of the fuel, and preferably 0.05% or less, more preferably0.03% or less, such as 0.01% or less, most preferably 0.005% or less andespecially 0.001% or less. Such fuels may be made by means and methodsknown in the fuel-producing art, such as solvent extraction,hydrodesulphurisation and sulphuric acid treatment.

As used in this specification, the term “middle distillate fuel oil”includes a petroleum oil obtained in refining crude oil as the fractionbetween the lighter kerosene and jet fuels fraction and the heavier fueloil fraction. Such distillate fuel oils generally boil within the rangeof about 100° C., eg 150° to about 400° C. and include those having arelatively high 95% distillation point of above 360° C. (measured byASTM-D86). In addition, “city-diesel” type fuels, having lower finalboiling points of 260-330° C. and particularly also sulphur contents ofless than 200 ppm (and preferably 50 ppm and particularly 100 ppm(wt/wt)) are included within the term ‘middle distillate fuel oil’.

Middle distillates contain a spread of hydrocarbons boiling over atemperature range, including n-alkanes which precipitate as wax as thefuel cools They may be characterised by the temperatures at whichvarious %'s of fuel have vaporised (‘distillation profile’), e.g. 50%,90%, 95%, being the interim temperatures at which a certain volume % ofinitial fuel has distilled. They are also characterised by pour, cloudand CFPP points. as well as their initial boiling point (IBP) and 95%distillation point or final boiling point (FBP). The fuel oil cancomprise atmospheric distillate or vacuum distillate, or cracked gas oilor a blend in any proportion of straight run and thermally and/orcatalytically cracked distillates. The most common middle distillatepetroleum fuel oils are diesel fuels and heating oils. The diesel fuelor heating oil may be a straight atmospheric distillate, or it maycontain minor amounts, e.g. up to 35 wt %, of vacuum gas oil or crackedgas oils or of both.

Heating oils may be made of a blend of virgin distillate, eg gas oil,naphtha, etc and cracked distillates, eg catalytic cycle stock. Arepresentative specification for a diesel fuel includes a minimum flashpoint of 38° C. and a 90% distillation point between 282 and 380° C.(see ASTM Designations D-396 and D-975).

As used in this specification, the term ‘middle distillate fuel oil’also extends to biofuels, or mixtures of biofuels with middle distillatepetroleum fuel oils.

Biofuels, ie fuels from animal or vegetable sources are believed to beless damaging to the environment on combustion, and are obtained from arenewable source. Certain derivatives of vegetable oil, for examplerapeseed oil, eg those obtained by saponification and re-esterificationwith a monohydric alcohol, may be used as a substitute for diesel fuel.It has recently been reported that mixtures of biofuels, for example,between 5:95 and 10:90 by volume are likely to be commercially availablein the near future.

Thus, a biofuel is a vegetable or animal oil or both or a derivativethereof.

Vegetable oils are mainly trigylerides of monocarboxylic acids, eg acidscontaining 10-25 carbon atoms and of the following formula:

wherein R is an aliphatic radical of 10-25 carbon atoms which may besaturated or unsaturated.

Generally, such oils contain glycerides of a number of acids, the numberand kind varying with the source vegetable of the oil.

Examples of oils are rapeseed oil, coriander oil, soyabean oil,cottonseed oil, sunflower oil, castor oil, olive oil, peanut oil, maizeoil, almond oil, palm kernel oil, coconut oil, mustard seed oil, beeftallow and fish oils. Rapeseed oil, which is a mixture of fatty acidsparticularly esterified with glycerol, is preferred as it is availablein large quantities and can be obtained in a simple way by pressing fromrapeseed.

Examples of derivatives thereof are alkyl esters, such as methyl esters,of fatty acids of the vegetable or animal oils. Such esters can be madeby transesterification.

As lower alkyl esters of fatty acids, consideration may be given to thefollowing, for example as commercial mixtures: the ethyl, propyl, butyland especially methyl esters of fatty acids with 12 to 22 carbon atoms,for example of lauric acid, myristic acid, palmitic acid, palmitoleicacid, stearic acid, oleic acid, petroselic acid, ricinoleic acid,elaeostearic acid, linoleic acid, linolenic acid, eicosanoic acid,gadoleic acid, docosanoic acid or erucic acid, which have an iodinenumber from 50 to 150, especially 90 to 125. Mixtures with particularlyadvantageous properties are those which contain mainly, ie. to at least50 wt % methyl esters of fatty acids with 16 to 22 carbon atoms and 1, 2or 3 double bonds. The preferred lower alkyl esters of fatty acids arethe methyl esters of oleic acid, linoleic acid, linolenic acid anderucic acid.

Commercial mixtures of the stated kind are obtained for example bycleavage and esterification of natural fats and oils by theirtransesterification with lower aliphatic alcohols. For production oflower alkyl esters of fatty acids it is advantageous to start from fatsand oils with high iodine number, such as, for example, sunflower oil,rapeseed oil, coriander oil, castor oil, soyabean oil, cottonseed oil,peanut oil or beef tallow. Lower alkyl esters of fatty acids based on anew variety of rapeseed oil, the fatty acid component of which isderived to more that 80 wt % from unsaturated fatty acids with 18 carbonatoms, are preferred.

The above described biofuels may be used in blends with middledistillate petroleum fuel oils. Such blends typically contain 0 to 10%by weight of the biofuel and 90 to 100% by weight of the petroleum fueloil, although other relative proportions may also be used toadvantageous effect. Particularly useful are blends of biofuels with‘city-diesel’ type fuel oils which exhibit extremely low levels ofsulphur and are therefore particularly prone to lubricity problems.

In the fuel oil composition of the sixth aspect, the concentration ofthe compound incorporated into the oil may for example be in the rangeof 0.5 to 1,000 ppm of additive (active ingredient) by weight per weightof fuel, for example 1 to 500 ppm such as 10 to 200 ppm by weight perweight of fuel, preferably 10 to 100 ppm, more preferably 15 to 50 ppm.

In addition to middle distillate fuel oils, other fuels having a needfor increased lubricity, such as fuels (e.g. future gasoline) intendedfor high pressure fuel injection equipment, may suitably be treated withthe additives of the invention.

The Fuel Oil Composition of the Second Aspect of the Invention

C The Additive Composition

The additive composition defined under the second aspect is prepared bythe incorporation of the compound into a composition itself comprisingone or more additives for fuel oils. Such incorporation may be achievedby blending or mixing, either with an existing composition or with thecomponents thereof, to produce the additive composition of the firstaspect of the invention. However, the term ‘incorporation’ within themeaning of this specification extends not only to the physical mixing ofthe compound with other materials, but also to any physical and/orchemical interaction which may result upon introduction of the compound,or upon standing.

Many fuel oil additives are known in the art and may be used to form thecomposition into which the compound is incorporated. Such additivesinclude for example the following; detergents, antioxidants, corrosioninhibitors dehazers, demulsifiers, metal deactivators, antifoamingagents, cetane improvers, combustion improvers, dyes, packagecompatibilisers, further lubricity additives and antistatic additives.Cold flow-improving additives may also be present.

D The Additive Concentrate Composition

The concentrate may be obtained by incorporating the compound or theadditive composition into a mutually-compatible solvent therefor. Theresulting mixture may be either a solution or a dispersion, but ispreferably a solution. Suitable solvents include organic solventsincluding hydrocarbon solvents, for example petroleum fractions such asnaphtha, kerosene, diesel and heating oil; aromatic hydrocarbons such asaromatic fractions, eg. those sold under the ‘SOLVESSO’ tradename; andparaffinic hydrocarbons such as hexane and pentane and isoparaffins.

Further solvents include oligomers and hydrogenated oligomers of alkenessuch as hydrogenated decene-1 dimer or trimer. Also useful are alcoholsand esters especially higher alcohols such as liquid alkanols having atleast eight carbon atoms. An especially useful solvent is isodecanol.Mixtures of such solvents maybe used in order to produce amutually-compatible solvent system.

The concentrate may contain up to 80% by weight, for example 50% ofsolvent.

The concentrate is particularly convenient as a means for incorporatingthe additive composition of the first aspect into fuel oil where despitethe presence of the compound, the co-presence of other additives in thecomposition demands an amount of solvent in order to imparthandleability. However, concentrates comprising the compound as soleadditive may also be used, especially where small quantities ofadditives are required and the equipment present for introduction of theadditive lacks the necessary accuracy to measure or handle such smallvolumes.

As indicated above, the compound defined under the first aspect, and theadditive composition and concentrate defined under the second aspect,find application in low sulphur fuel oils.

A further aspect of this invention is therefore the use of the compound,or the additive composition or concentrate, in a liquid hydrocarbonmiddle distillate fuel oil, having a sulphur concentration of 0.2% byweight or less, per weight of fuel, particularly to improve thelubricity thereof. This invention also provides a method for improvingthe lubricity of a liquid hydrocarbon middle distillate fuel oil havinga sulphur concentration of 0.2% by weight based on the weight of fuel,comprising the addition thereto of the additive composition orconcentrate, or of the compound.

Where the fuel oil composition is produced by incorporation of theadditive or concentrate composition, the amount used of each of thesecompositions will be such as to ensure the incorporation to the fuel oilof the requisite amount of the compound. For example, however, theamount of additive or concentrate composition will usually be in therange of 1 to 5,000 ppm (active ingredient) by weight per weight offuel, especially 10 to 2000 ppm such as 50 to 500 ppm.

The Compound of the Third Aspect

The compound claimed under the third aspect comprises one or morehydroxyl derivatives of the formula —OR′ wherein R′ is as defined inrelation to the first aspect but is not hydrogen. Such materials mayshow good performance as lubricity improvers and as detergents and/ordispersants in low sulphur middle distillate fuel oils.

The invention will now be described further by reference to the examplesonly as follows:

EXAMPLE 1 Preparation of the Compounds

Compounds as defined under the first aspect of the invention wereprepared via esterification of hydrocarbyl-substituted salicylic acidcompounds with 1,2-dihydroxy ethane (ethylene glycol). The syntheticprocedures used are given below.

In each case, the hydrocarbyl substituents on the salicylic acid weren-alkyl groups ranging in carbon number from 14 to 18 and predominatelyC18 alkyl. Most of the salicylic acid reactant was mono alkylatedalthough a proportion was dialkylated with two such alkyl groups.

Ester A

In a 5-necked round bottom flask equipped with a mechanical stirrer, anitrogen sparge and a Dean-Stark condenser were placed 100 g ofalkylsalicylic acid (65% Al in xylene, total acid number of 87.2 mgKOH/g), 32.6 gms of 1,2-dihydroxyethane, 100 g of toluene and 1.5 g ofparatoluenesulphonic acid. The mixture was heated at reflux temperaturefor 6 hours and then transferred to a rotary evaporator. The product wasdried at 130° C. under vacuum. The TAN of the final product was 88.4 mgKOH/g corresponding to 33% conversion of the acid to ester product.

Ester B

The procedure for ester A was repeated except that the toluene wasreplaced by the same amount of solvent 30 (an aliphatic solvent). TheTAN of the final product was 86.7 mg KOH/g corresponding to 35%conversion of the acid to ester product.

The reaction products of these syntheses thus showed, by TAN, incompleteesterification ie. some unreacted acid remained in the end product.

A further esterification product was obtained by the transesterificationof the methyl ester of the substituted salicylic acid used for esters Aand B by 1,2-dihydroxyethane, as described below.

Ester C

(i) Preparation of the methyl ester of alkyl salicylic acid

In a 5 necked round bottom flask equipped with a mechanical stirrer, anitrogen sparge and a Dean-Stark condenser were placed 329 g ofalkylsalicylic acid (65% Al in xylene), 349 g of methanol and 16.7 g of90% sulfuric acid. The mixture was refluxed at 65-66° C. for 16.5 hours.

The mixture was concentrated by boiling off 322 ml of methanol leadingto a phase separation of the mixture. The reaction mixture was decantedinto a separating funnel and the bottom layer, approximately 40 mlconsisting of xylene and sulfuric acid, was removed. The top layer waswashed 5 times with 100 ml of distilled water and finally dried in arotary evaporator at 118° C. to give 203 g of material with a TAN of81.3 mg KOH/g.

(ii) Transesterification reaction

In the same 5 necked flash were placed 75 g of the previously preparedmethyl ester, 145 g of 1,2-dihydroxyethane and, 232 g of solvent 30 and2 g of paratoluenesulfonic acid. The mixture was heated under reflux at107° C. for 10 hours. The volatile solvents and unreacted material werethen removed using a rotary evaporator at 130° C. to give 81 g ofmaterial with a TAN of 72.7 mg KOH/g corresponding to a 45% conversionof the acid to ester product.

A fourth esterification product was prepared by an epoxide ring-openingreaction using glycidol (1-hydroxy-2,3-epoxypropane).

Ester D

To a 3 necked flask was added 100 g of the alkylsalicylic acid (TAN of129 mg KOH/g), 100 g of toluene and 0.058 g of lithium hydroxidemonohydrate. The mixture was heated at 105° C. whilst glycidol (16 g )was added dropwise with a dropping funnel over a 4.5 hours period. Themixture was then stripped in a rotary evaporator at 90° C. The finalmaterial has a TAN of 26.4 mg KOH/g corresponding to 80.4% conversion ofthe acid to ester product.

EXAMPLE 2 Lubricity Performance

Esters A, B, C and D were added to a low sulphur middle distillate fueloil having the following characteristics:

Density @ 15° C. 0.8256 Cloud Point, ° C. (CP) −11 WAT ° C. −14.62 % Wax@ 5° C. below CP 1.58 % Wax @ 10° C. below CP 2.78 Sulphur, ppm, w/w210.9 HFRR @ 60° C. (wear scar diameter) 548 μm D86 Distillation IBP 157 5% 186 10% 194 20% 208 30% 222 40% 237 50% 251 60% 266 70% 280 80% 29690% 315 95% 328 FBP 345 FBP-90% 30 90%-20% 107

The resulting fuel oil compositions were tested in the High FrequencyReciprocating Rig Test (or “HFRR”) for lubricity performance andcompared to a sample of the fuel oil treated with salicylic acid(Comparative No 1), and a sample treated with an ester mixture preparedby esterification of a commercial mixture of oleic and linoleic acidswith glycerol (Comparative No 2). The mixed ester product of ComparativeNo. 2 predominated in (a) glycerol monooleate and (b) glycerolmonolinoleate, in approximately equal proportions by weight, with minoramounts of glycerol di- and trioleate and linoleate also present. Inaddition, the commercial acid mixture used to make this comparativeadditive contained a minor proportion of other acids, the esters ofwhich were not believed to represent more than about 6% by weight of themixed ester product. The HFRR test method is described in the industrystandard test methods CEC PF 06-T-94 and ISO/TC22/SC7/WG6/W188 and wasperformed at 60° C.

The amounts of each additive used and the results of the HFRR tests areshown in Table 1.

TABLE 1 Additive Treat Rate HFRR Wear Scar Diameter (μm) at 60° C. (ppmactive Ingredient w/w) Comparative No. 1 Ester A Ester B Ester C Ester DComparative No. 2 0 548 548 548 548 548 548 7.3 506 7.6 562 9.9 503 13.8387 14.6 353 15.2 380 17.6 336 19.8 331 21.5 541 24.7 333 25.0 494 29.2355 30.4 340 35.3 276 42.9 533 50.0 414 58.4 355 60.8 394 79.0 335 85.8395 100.0 252 141.0 171.6 350 346

In the Table, no entry at a particular treat rate means no measurementwas made at that treat rate for that additive.

The active ingredient levels tested for each additive varied slightlydue to the differences in conversion obtained in each synthesis.

In conclusion, it can be seen that compositions comprising the compounddefined under the first aspect of the invention were surprisingly morepotent as lubricity additives in comparison to other esters.

EXAMPLE 3 Handleability

The handleability of esters A and C as prepared above were compared withthat of the reactant alkylsalicylic acid and with a commercial lubricityadditive comprising a mixture of oleic and linoleic acid esters ofglycerol (Comparative No. 2 from Example 2).

In each case, the material was stored at −10° C. in both undiluted anddiluted form and the appearance and behaviour noted after 42 days,simulating field storage during a substantial period of cold weather.The results are shown in Table 2.

TABLE 2 % wt Aromatic Appearance/Behaviour Additive Solvent (diluent)after 42 days @ −10° C. Ester A 0 Homogeneous-mobile liquid 30Homogeneous-mobile liquid 50 Homogeneous-mobile liquid Ester C 0 A fewcrystals formed 30 Homogeneous-mobile liquid 50 Homogeneous-mobileliquid C₁₄₋₁₈ Alkylsalicylic 0 Phase separation Acid 30 Crystals formed50 Hazy mixture Commercial Glycerol 0 Solid Esters Mixture 30 Phaseseparation 50 A few crystals formed

The esters A and C thus showed significantly better cold temperaturestorage properties, both in diluted and undiluted form, indicatingbetter handleability in the absence of heating and mixing equipment.

What is claimed is:
 1. A fuel oil composition obtainable by theaddition, to a major proportion of a liquid hydrocarbon middledistillate fuel oil having a sulfur concentration of 0.2% by weight ofless, based on the weight of fuel, of a minor proportion of either (a) acompound of the general formula (I):

 wherein Ar represents an aromatic ring system; B represents ahydrocarbon group (i); OR′ represents a hydroxyl group or derivativethereof (ii) wherein R′ represents hydrogen, or a hydrocarbyl group, ora group of the formula

 wherein M represents an oxygen atom or an NH group and n represents anumber from 1 to 50, and wherein R′ may be bonded either directly to theoxygen depending from the ring system or indirectly via a linking group;—COOR″ represents an ester group (iii) wherein R″ represents an alkylgroup optionally substituted by one or more hydroxyl groups, and Arepresents a group of the formula (II):

 wherein Ar, B, R′ and R″ are as defined above, and A′ and A″ eachindependently represent hydrocarbylene groups, and wherein v representsan integer in the range of from 0 to 10, w represents an integer in therange of from 1 to 3, and x, y and z each independently represent aninteger in the range of from 1 to 3; (b) an additive compositioncomprising one or more additives for fuel oils and into which has beenincorporated the compound (a); or (c) an additive concentrate obtainableby incorporating the compound (a) or additive composition (b), andoptionally one or more additional additives, into a mutually-compatiblesolvent therefor.
 2. The composition of claim 1 wherein each aromaticring system of the compound is a single, six-membered ring.
 3. Thecomposition of claim 1 wherein the ester group comprises an alkyl orhydroxy-substituted alkyl substituent.
 4. A method for improving thelubricity of a liquid hydrocarbon middle distillate fuel oil having asulphur concentration of 0.2% by weight or by less based on the weightof fuel, comprising the addition thereto of the compound 15-50 ppm of oradditive composition or concentrate defined in claim 1.